The present invention relates to the production of heavy hydrocarbons and, particularly, with treating heavy hydrocarbons to lower their viscosity either in situ or at surface facilities.
Heavy and extra heavy hydrocarbons with an API.degree. gravity in the range between 6 and 12 and a dynamic viscosity of greater than 300 cps at 195.degree. F. are difficult to produce from a subterranean formation by conventional methods due to their high viscosity. Several methods are disclosed in the art for recovering these heavy hydrocarbons and transporting them to the surface. One of the most used techniques is the steam injection technique wherein the viscosity of the hydrocarbons is temporarily thermally reduced thereby improving the hydrocarbon flowability to the surface. The steam injection into the formation can be done either by continuous steam drive or by cycle injection techniques. Both methods suffer from the disadvantage of a low hydrocarbon recovery and, in most cases the viscosity of the hydrocarbons after treatment is higher than the viscosity of the in situ hydrocarbon in the reservoir.
To overcome the forgoing disadvantages, several steam additives have been disclosed in the art, such as solvents and gases, for simultaneous injection with steam. Solvents, such as kerosene, diesel fuel or the like, are added to the heavy hydrocarbon to reduce the front flow profile and thereby lowering the oil viscosity of same. Gaseous additives, such as carbon dioxide, are used with the steam injection to enhance heavy hydrocarbon recovery in what is known as "gas lifting" processes to assist the hydrocarbon mixture in its way up to the surface of the production well. In these processes, however, the viscosity reduction of the hydrocarbon is temporary and reverts to its original viscosity once at the surface of the well.
Prior art surface treatment of viscous hydrocarbons to make them pumpable include heating the hydrocarbon, high temperature-high pressure treatment of the hydrocarbon and by introduction of a solvent as described above. These prior art systems suffer from a number of disadvantages. Firstly, these treatment processes require complex equipment for the high temperature-high pressure treatments which is quite costly. In addition, it has been found in the case of high temperature treatment processes that there is an increase in coke production when carrying out distillation of the crude.
It is desirable to have a method for the in situ lowering of the heavy hydrocarbon viscosity to enhance its recovery from the subsurface and ensure that the viscosity of the hydrocarbon does not revert with time after the hydrocarbon has been brought to the surface and later pumped by conventional transportation systems.
At the same time, it is desirable to provide a method of improving the viscosity of a virgin heavy hydrocarbons at the surface so as to allow the hydrocarbon to be transported by conventional pipeline systems and stored and handled by conventional techniques.
Accordingly, it is the principle object of the present invention to provide a method for the in situ lowering of the viscosity of a heavy hydrocarbon downhole at the well formation.
It is a further principle object of the present invention to provide a method for lowering the viscosity of a virgin heavy hydrocarbon, at the surface production facility, so as to allow them to be transported by conventional equipment.
Further objects, advantages and features of this invention will become more apparent to those skilled in the art from the following description and appended claims.